A decade of movement ecology
Abstract (250 words - I’m at 286 now)
Movement affects population dynamics, biodiversity, and consequently, the structure of ecosystems. With the recent development of sophisticated tracking technology, software, and analyses, research in movement ecology has significantly increased in the last decade. We aimed to provide a synthetic and quantitative review of the scientific literature in movement ecology since the seminal work of Nathan et al. (2008), which formally introduced the movement ecology framework. We reviewed 5354 peer-reviewed papers in movement ecology published in the last decade. Using a text mining approach, we assessed the number of papers that have attempted to investigate core components of the movement ecology framework—that is, motion, navigation, internal state, and external factors—as well as the biologging devices used, the focal taxon, the analytical methods applied, and the software used. The changes in the devices and software used reflect an increasing access to finer spatio-temporal data about movement, with growing ability to process them. However, this is not reflected in the choice of statistical methods which are mostly general rather than movement-related. Even more importantly, and just like ten years ago, studies rarely explicitly focus on the components of the movement ecology framework (except for external factors). The research topics identified in the literature were organized around questions that corresponded to a mix between understanding theoretical movement processes, data collection and analysis, and practical applications. [SP: This sentence is unclear to me. I’m not sure what you meant] Based on these findings, we discuss how data and technology have been driving our science, research questions that have not been given enough consideration, and the necessary trade-off between theory and technology.
Nathan, R., Getz, W. M., Revilla, E., Holyoak, M., Kadmon, R., Saltz, D., & Smouse, P. E. (2008). A movement ecology framework for unifying organismal movement research. PNAS, 105(49), 19052–19059.
Keywords (min 3)
movement ecology, technology, text mining, biologging, human movement, …
The rise of a field called movement ecology (there shouldn’t be a title for the Introduction but I like this one)
Movement is intrinsically linked to life and has been a research subject since ancient times. [SP: How about citing the Aristotle De Motu Animalium that is in the timeline figure here?] Technological developments in the recent decades have opened possibilities to observe and collect data on animal and human movement, and to expand our knowledge on their distribution and behavior (Thums et al. (2018), Börger (2016), Williams et al. (2019)). In what is considered a seminal work in the field, Nathan et al. (2008) proposed a unifying conceptual framework for movement ecology, consisting of four components: external factors (i.e. the set of environmental factors that affect movement), internal state (i.e. the inner state affecting motivation and readiness to move), navigation capacity (i.e. the set of traits enabling the individual to orient), and motion capacity (i.e. the set of traits enabling the individual to execute movement). The outcome of the interactions between these four components would be the observed movement path (plus observation errors).
A concurrent study examined movement-related papers (Holyoak et al. (2008)), finding that very few works in the literature addressed the links between these components, with the only exception of external factors with motion capacity (62%). They found that the majority of studies were “simply measuring movement, documenting its ocurrence, or describing how it was influenced by the environment”.
Ten years after PNAS’ special feature on Movement ecology – where Nathan’s and Holyoak’s work were published – the number of studies in the field has increased exponentially (Fig. 1), several special issues related to the field have appeared in different journals, and there is now even a Gordon Research Conference on Movement ecology of animals organized every two years (since 2017). It is a good time [RJ: I’m looking for a synonym to the word kairos in Greek… any ideas?] [SP: How about “the time is ripe”?] to reflect on the status of research on this field, and to investigate the role of ideas (e.g. the movement ecology framework or MEF), data, and technology in the field, and what challenges await us.
[Comment MEB]: # (MEB: Just suggestions idk if they fit or not: pivotal, momentous, apropos, crucial, convenient, pertinent, oppurtune...actually felicitous might work to mean just that)
{Fig.1. Timeline of movement ecology papers and milestones in the field}
For this purpose, we reviewed the field of movement ecology using a quantitative approach. With a hierarchy of keyword-based filters, we searched the Web of Science for movement ecology papers published in 2009-2018, and analyzed the text in the manuscripts to assess which aspects of movement ecology were being studied and the tools that were being used. All the technical details of the text analysis can be found in Supplementary Materials and the R code in [RJ: Zenodo repository].
The document is organized as follows. First, we analyzed the MEF and quantified the study of its different components in the literature within the past decade. Then, we assessed the use of different tools (i.e. biologging devices, software, and statistical methods) in the papers. Next, we identified topics and research subjects that papers addressed. Finally, with all these elements in hand, we provided an integrative view of the field, its strengths, limitations, and future directions.
The movement ecology framework
Most movement ecology studies in the past decade have addressed the relationship between external factors and movement (77%), and a minority of them have studied the three other components of the MEF (49%, 26% and 9%, for internal factors, motion and navigation capacity, respectively). [SP: I wouldn’t call 49% a minority…] The same pattern occurred in the decade before (see Supp. Mat), reflecting that, in the last ten years, movement ecologists have not increased their efforts to understand the processes behind movement. The focus on external factors, and particularly on the environment (Table 1), might be a result of having management and conservation as an ultimate goal from understanding movement (Allen and Singh (2016); Ogburn et al. (2017)).
[Comment 2]: # (RJ: Tommy asked for time series. They are in the Supp. Section. There is not much change in time. I am also putting the framework figures (from each decade) in Supp. but we can take them out if there if you think that they are key in the manuscript.)
[Comment 3]: # (RJ: Mathieu made interesting comments, that I copy here. I prefer if he edits directly in the text, or someone else. "MB: Despite repeated calls to figure out the mechanics of movement, we're essentially still doing descriptive studies, relating space use to the environment. I would think that one essential reason for this is management and conservation. We work with habitats, areas—in fact, not species. So the most important piece for management/conservation is the link to the physical environment, which is really what we're managing/protecting (probably for good and bad reasons). *Fundamental movement ecology* remains a niche.")
[Comment MEB]: #(MEB: I was having similiar ideas on the drivers here. And in my gut I want to say that this is tied back to what is funded, but I can't find any resources to prove the point that one type of research is funded over the other. These internal questions just dont seem to have strong ties back to the physical world/conservation so it makes sense theyre not studied in depth.)
[Comment 8]: # (SP: I like what Mathieu said above, and I would even take it one step further: the very etymology of the word "ecology" comes from "oikos" and "logos", which is "the study of the home" which in other words means the study of the environment. The definition of ecology by Ernst Haeckel (1866) is "All the comprehensive science of the relationship of the organism to the environment". So ecology is inherently focused on the environment. Dealing with the internal state of an animal is closer to ethology than it is to ecology. Motion capacity is closer to biomechanics. Navigation is closer to neuroscience. But ecology is inherently environmental. To me it's pretty natural that ecologists spend all their time thinking about the effect of external factors on animals.")It is not only more practical but also easier to observe and collect data from external factors like the environment, other individuals or humans. There are satellite data on environmental features, and animal interaction – in some cases – could be observable, and human pressure could be accounted for if there are data from before and after some kind of impact (e.g. noise or urbanization). Conversely, physiological, behavioral syndrome, biophysical, and orientation aspects, among others, may need additional data on body conditions or controlled environments to make tests. [SP: But we have a lot of this from biologging devices such as heart-rate monitors, accelerometers, vital rates sensors, etc… There was a whole special feature of JAnE on combined sensors for biologging last year.] Out of the four components of the MEF, navigation was the least studied. Understanding how animals orient in space, using cues and memory may be one of the most challenging tasks in movement ecology. Although advances have been made (e.g. regarding the use of magnetic and sun compass, or the use of odour by many animal species; Hansson and Akesson (2014)), many challenges remain, like understanding how the information is processed by the brain, or obtaining olfactory or sound landscapes data to test hypotheses in the field.
Studying any of these components and thus understanding the movement process of organisms require integrative and multidisciplinary efforts involving ecologists, biologists, neuroscientists, physicists and statisticians, to cite some examples. [SP: Yes! I like this point. Goes well with what said above that some of the MEF components are not strictly the job of ecologists…] Because of satellite data availability, a practical need for multidisciplinarity could be lower for external factors. [SP: Not only because of satellite data availability, but also because studying the effect of external factors on organisms is essentially what ecology is] All of these reasons (interest for conservation, data availability, less need for multidisciplinary work) could explain that the majority of movement ecology studies are related to external factors. This pattern was seen in all animal taxonomical groups, except in humans, for which the studies were more uniformly distributed between external factors, internal state and motion (see Fig. 2). For humans, studies would not respond to practical conservation purposes but rather to health and movement efficiency, which involve internal aspects (e.g. nutrition, heart rate, respiration) and motion (e.g. locomotion and biomechanics). [SP: Which reinforces the point above: these studies are not in ecology] The necessary data is also easier to obtain from humans, since they could be directly interested in improving their health (e.g. patients) and increase their movement power (e.g. sport players).
[Comment 4]: # (RJ: If you disagree with what I wrote or find it confusing, please let me know. And feel free to modify the text and complement it with your ideas. )| External factor | Percentage | Internal factor | Percentage | Motion capacity | Percentage | Navigation capacity | Percentage |
|---|---|---|---|---|---|---|---|
| Environment | 80.7% | Adaptation | 45.9% | Empirical | 50.9% | Orientation | 73.6% |
| Animal interaction | 38.1% | Life-history | 42.2% | Biophysical | 36.3% | Cognitive | 25.5% |
| Anthropogenic | 13.6% | Physiological state | 34.5% | Theoretical | 32.1% | Sensory | 7.6% |
| Other | 3.3% | Behavior | 7.2% | ||||
| General | 0.4% | General | 1.6% |
Table 1. Categories in which each component of the movement ecology framework is split. The percentages are computed as the number of abstracts referring to the category divided by the number of abstracts concerning the correspondent component, multiplied by 100.
[Comment 5]: # (RJ: Tommy, can you improve the caption of Table 1 explaining the elements that need explanation? Or simply point at the link to the readme. Whatever you think it's best, if you think we should keep this table here.)
[Comment MEB]: # (MEB: I can not read this table well at all. Partially it can be displayed better (colors or physical dividers between categories/columns), also better explained in the caption (as mentioned). For instance I cant figure out whats supposed to add up to 100%, what isnt, and why any of that is)
{Fig.2. Sankey plot showing the distribution on papers concerning the different taxonomical groups, framework components and main topics. Line segment thickness is the relative number of papers sharing two categorical nodes (e.g. About 50% of mammal papers are about external factors, where as only 30% of external papers were about mammals). *Humans are considered as a separate group for interpretation.}
[Comment 6]: # (RJ: Matt, can you add a very short explanation of how to read the Sankey plot in the caption?)Tools for movement ecology
( (original){ Technology has been a major driver in movement ecology. Literature reviews highlight a growing trend in the amount and variety of tracking devices, which are becoming more afordable, with more-efficient parametrization for battery saving and shrinking in size (Thums et al. (2018), Kays et al. (2015), Harcourt et al. (2019)). Here we categorized tracking device observations as accelerometer, acoustic telemetry (referred to as “acoustic”), body condition measurements (“body conditions”), encounter observations (“encounter”), GPS (handheld devices and tagged devices), light loggers, pressure data, radar, radio telemetry, satellite and video/image (“video”). Details of these categories and the analysis are in Supp. Mat. Throughout this last decade, GPS has not only remained the most popular device in movement studies, but its use has increased (in proportion to the total number of studies, see Fig. 3). This is likely due to the development of smaller and more efficient devices, which make them a good option for small and medium size animals (Kays et al. (2015)), particularly mammals and birds (see Fig. S10 and S11 in Supp.Mat.). GPS could also be replacing radio telemetry (Allan et al. (2018)), which has been experiencing a decreasing trend. On the other hand, the use of accelerometers and video is becoming more popular in the field, allowing for finer spatio-temporal resolution movement data (Fig. 3). } (simonas){ Technology has been a major driver of discovery in movement ecology. Literature reviews highlight a growing trend in the amount and variety of tracking devices, which are becoming more afordable, with more efficient parametrization for battery saving, and shrinking in size (Thums et al. (2018), Kays et al. (2015), Harcourt et al. (2019)). Here ,we categorized tracking device observations as accelerometer, acoustic telemetry (referred to as “acoustic”), body condition measurements (“body conditions”), encounter observations (“encounter”), GPS, light loggers, pressure data, radar, radio telemetry, satellite, and video/image (“video”). Details of these categories and the analysis are in Supp. Mat. Throughout this last decade, GPS has not only remained the most popular device in movement studies, but its use has increased (in proportion to the total number of studies, see Fig. 3). This is likely due to the development of smaller and more efficient devices, which make them a feasible option for small and medium-sized animals (Kays et al. (2015)), particularly mammals and birds (see Fig. S10 and S11 in Supp.Mat.). GPS could also be replacing radio telemetry (Allan et al. (2018)), which has been experiencing a decreasing trend. On the other hand, the use of accelerometers and video is becoming more popular in the field, allowing for finer spatio-temporal resolution movement data (Fig. 3). [SP: I don’t think that the point of accelerometers and video is to increase spatio-temporal resolution, rather they provide different types of data.] }
[Comment MEB]: # (MEB: I do have to caution that we have no idea that amount of these papers that used hand held gps devices versus tags. I would not be confident in saying which one is the majority. If this is an issue we might have to seperate them into two new categories and try to search 'hand held GPS' and 'gps & tag'. Thats if we can find the right words to separate the categories well. I'm not sure.)
[Comment MEB]: # (Also as soon as we figure out what graphs we want I'll need to work on all these line graphs, aesthetically. There should be a better way to show off what we want)